1. Technical Field of the Invention
The present invention relates to the monitoring of telephone calls by law enforcement agencies and, in particular, to the selection of a preferred connection between a monitoring center and one of the parties to a monitored telephone call.
2. Description of Related Art
It is well known in the art for law enforcement agencies to tap telecommunications trunk connections for the purpose of monitoring voice conversations and data transmissions (calls). Telecommunications switches in the network are programmed with a stored list of telephone numbers assigned to subscribers whose calls are to be monitored. Whenever a group switch handles a call connection having a calling party or called party identification number matching a number on the stored list, the group switch establishes a connection (comprising the xe2x80x9ctapxe2x80x9d) with a monitoring center. Voice or data signals from the calling party side are monitored using a first switch connection, while monitoring of the voice or data signals from the called party side requires a second switch connection.
Typically, if the request for the establishment of the tap is granted, the group switch routes the first and second switch connections to a conference call device, which mixes the signals from the first and second switch connections. The group switch then establishes a single connection to the monitoring center over which the mixed signal is routed. The monitoring center receives the mixed signal and feeds it to a recording device or some type of monitoring sensor.
In some instances, it is desirable to establish two or more separate tap connections to the monitoring center (i.e., one connection for each of the parties). In this case, when a switch handles a call connection having a calling party or called party identification number matching a number on the stored list, the switch establishes a first connection with the monitoring center for the calling party side and a second connection with the monitoring center for the called party side of the communication. The monitoring center feeds these connections to separate recording devices or monitoring sensors. This arrangement allows the law enforcement agency to, for example, easily distinguish which signals are originating from each of the parties.
In existing monitoring systems that use the two connection scenario, however, problems sometimes arise with the setup of one of the two connections. The connection request can fail, for example, because the particular monitoring center number towards which the switch directs the connection request is busy or because there is a malfunction in the telecommunications network or in the monitoring center. Thus, a connection is established for one of the parties but not for the other. When one of the connection requests fails in this manner, the remaining connection or connections are dropped, and neither party to the conversation or data transmission is monitored. There are situations, however, in which it is desirable to continue monitoring the signals originating from one of the parties even when monitoring of another party is not possible. Thus, there is a need for a method and system for maintaining one monitoring connection to a call and for enabling monitoring of a selected one of the parties when a second monitoring connection to the call fails.
The present invention comprises a method and apparatus for monitoring a call connection by a law enforcement agency involving the reselection of a monitoring trunk to provide monitoring of a primary party to a call connection. In accordance with the invention, a list of directory numbers marking those subscribers to a telephone network whose calls are to be monitored is stored in a network switching node. Each time a call setup request is received in the switching node, the calling party and called party directory numbers contained in the request are compared against the stored list of xe2x80x9cmarkedxe2x80x9d subscribers. When a call setup request is received involving one or more xe2x80x9cmarkedxe2x80x9d subscribers, the call is identified as a call to be monitored. A group switch that is handling the call connection attempts to set up separate connections with a monitoring center for each of the parties to the call to be monitored. Generally, data or voice transmissions from each of the parties to the call are received by the group switch at a particular multiple point (MUP). By establishing a connection between the particular MUP associated with each party to the call and a respective monitoring center, each party can be separately monitored. This ability to separately monitor the parties is particularly valuable in the case of data transmissions, where it is often difficult to distinguish the source of a data transmission if the parties"" transmissions are mixed on a single monitoring connection with the monitoring center.
In some cases, however, one of the separate attempted connections fails. There are two methods for addressing this problem in accordance with the present invention. In the first method, a determination is made as to which party is the primary party to be monitored. The primary party is determined according to preselected criteria stored at the switching node. Once a failure of one of the multiple attempted connections is detected, it is determined whether the primary party connection is the failed connection. If not, the successful connection(s) are maintained and those portions of the call associated with the successful connection(s) (including signals received from the primary party) are monitored. If the primary party connection has failed, however, the group switch reroutes signals from the primary party to a successful connection. Accordingly, a new connection within the switch is established connecting the primary party MUP with a successful connection between the group switch and the monitoring center, and monitoring of the primary party is provided.
In the second method for dealing with a failed connection, it is first determined which party to the call is the primary party according to preselected criteria. Signals received at the MUP associated with the primary party are then routed to the first successful connection between the group switch and the monitoring center. Again, monitoring of at least the primary party is provided.